The measurement of characteristics of each chip of a semiconductor wafer, on which a plurality of chips having a fixed pattern are formed at a predetermined pitch a (hereinafter referred to as wafer), is usually performed using a wafer prober. In this case, the wafer with the chips to be measured is placed on an X-Y stage, and the characteristics of each chip are measured with the wafer prober by moving the wafer along the X-Y stage in an X-direction (transversal direction) or Y-direction (longitudinal direction) at the pitch a noted above. In this case, if the pitch a, at which the individual chips are arranged, is exactly the same as the pitch a', at which the wafer is moved along the X-Y stage, the wafer prober is set to a position corresponding to a given chip on the wafer when the wafer is moved a predetermined distance in the X-direction. Thus, there occurs no positional deviation between the wafer prober and the chip to be measured. Actually, however, mechanical errors occur in driving the X-Y stage and other parts as well as errors caused in the X-Y stage and other parts due to temperature variations at the time of the measurement. Therefore, there arises an error .DELTA.a between the actual pitch a' of the movement of the wafer and the arrangement pitch of the chips. Therefore, when the wafer is moved N times in a predetermined direction, an accumulation error of .DELTA.a.times.N is produced. Further, the wafer sometimes has a fixing distortion produced in a photolithographic step, and in this case it is possible that the individual chips fail to be arranged correctly on the wafer. In such a case, when the wafer is moved along the X-Y stage, the wafer prober is liable to be set at a position deviated from the chip to be measured.
Heretofore, as a method of correcting such errors, there is one, in which the accumulation error produced in correspondence to the movement of the wafer is measured using a microscope, and then either (1) a screw of a drive motor of the X-Y stage for determining the extent of movement of the wafer is caused to be moved a predetermined distance in a predetermined direction or (2) the revolving rate of the drive motor is controlled.
In method (1), the drive motor is used to determine the distance which the wafer is moved in the X-direction, in accordance with the movement of a screw nut used for connecting the screw and the X-rails together. If the screw and the X-rails are set in parallel to each other, the screw nut is allowed to move to the maximum degree. If the screw and the X-rails are set within a certain angle therebetween, the degree of movement of the screw nut is limited, in comparison with the case where the screw nut and the X-rays are set parallel. In this way, the drive motor is used to determine the moving distance of the wafer by merely changing the setting direction of the screw nut, i.e., without the need to change the revolving rate of the motor.
In method (2), for every movement of the wafer the revolving rate of drive motor M is controlled to vary the extent of movement of the wafer in the X-direction.
Method (1), however, involves a very large number of steps. Further, in both methods (1) and (2), the error is measured with a microscope, and the operator corrects the extent of movement of the wafer according to the measured value of error. Therefore, the measurement of error requires great time and labor. Further, it is impossible to correct errors due to the measured temperature or material of the wafer. Furthermore, since the error accumulation corresponding to the measured errors is corrected, errors in the arrangement of chips, which are produced in the photolithographic step and are not related to the movement of the wafer, can not be corrected.